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Runaway star creates bow shock as it speeds through galaxy

Kappa Cassiopeiae speeds through the galaxy at 1,100 kilometers per second. It creates this bow shock, which is about 4 light-years ahead of its star.

Bright blue star at center of this image is Kappa Cassiopeiae – a visible star in the constellation Cassiopeia the Queen – 4,000 light-years away. What you’re seeing here is an infrared bow shock, created by this star as it speeds through the galaxy at 1,100 kilometers per second. Image via NASA.

This is a star map of the familiar M or W shape of the constellation Cassiopeia, with the star Kappa Cassiopeiae circled. Via Wikimedia Commons

This newly released image from NASA’s Spitzer Space Telescope shows Kappa Cassiopeiae, a visible star in the constellation Cassiopeia the Queen. It is a massive, hot supergiant moving at around 2.5 million mph relative to its neighbors (that’s 1,100 kilometers per second, in contrast to about 30 miles per second for the speed of our Earth in orbit around the sun). See the streaky red glow of material in its path? That is the bow shocks from Kappa Cassiopeiae, moving ahead of its star – 4 light-years ahead – as the star speeds through our Milky Way galaxy.

Bow shocks can often be seen in front of the fastest, most massive stars in the galaxy. They form where the magnetic fields and wind of particles flowing off a star collide with the diffuse, and usually invisible, gas and dust that fill the space between stars.

How these shocks light up tells astronomers about the conditions around the star and in space. Slow-moving stars like our sun have bow shocks that are nearly invisible at all wavelengths of light, but fast stars like Kappa Cassiopeiae create shocks that can be seen by Spitzer’s infrared detectors.

Think how incredible it is that this shock is created about 4 light-years ahead of Kappa Cassiopeiae. This is about the same distance that we are from Proxima Centauri, the next-nearest star to our Earth and sun.

Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.